Yes you need carbs post workout. Lots of them. As far as the carb source, it really doesn't matter. I think Bobo recommends low gi carbs such as oats. I've always used dex/malto, but I might try oats to see if there is a noticable difference between the two.

the question is though, does my ON 100%whey protein already have some sort of fast acting carb in their concoction?

it should have some sugar in it. but that is not enough for post cycle. Lots of people like to blend their oats within their shake so the oats resemble a liquidy mush within their protein, therefore passes through the digestive system quicker. I normally have oats and maybe some fruit for post cycle.

so oats are a low gi carb, which gets absorbed slowly, so I put that in my PWO shake?
I do put oats in shakes, but not my PWO shake because I was under the impression that oats would prolong the absorption of the protein shake. (when in fact I was wrong and it is the total opposite)